1. Field of the Invention
The present invention relates to a remote commander for controlling audio-visual device such as a television receiver and a video tape recorder by using an infrared light-emitting diode from a distance.
2. Description of the Related Art
Heretofore, there has been proposed a remote commander for controlling audio-visual devices such as a television receiver (TV) and a video cassette recorder (VCR) by using an infrared light-emitting diode from a distance. FIG. 1 shows an outward appearance of such remote commander.
FIG. 2 is a diagram showing a circuit arrangement of such related-art remote commander. As shown in FIG. 1, there is provided a key device 1 including a keypad on which there are disposed various keys such as a power key, numerical keys and a volume control key. When a user operates a certain key on the keypad of the key device 1, a key signal corresponding to depression of a certain key is generated from the key device 1 and supplied to a switching signal generating circuit 2. The switching signal generating circuit 2 formed by a microcomputer modulates a carrier pulse having a frequency of 40 kHz in response to a key signal in a predetermined modulation manner to generate a switching signal. A duty ratio of this carrier pulse is generally selected to be 1/3.
A switching signal obtained at the output side of the switching signal generating circuit 2 is supplied to the base of an npn transistor 3 comprising a switching element so that the npn transistor 3 is turned on and off in response to the carrier pulse of this switching signal. The emitter of the npn transistor 3 is connected to the ground, the collector of the npn transistor 3 is connected to the cathode of an infrared light-emitting diode 4, and the anode of the infrared light-emitting diode 4 is connected through a current-restriction resistor 5 to a power supply at a terminal 7, to which a supply voltage Vcc is connected.
As shown in FIG. 3, in the infrared light-emitting diode 4, an intensity of a light output Po emitted from the infrared light-emitting diode 4 is in proportion to a current I, and the light output Po increases as the current I flowing through the infrared light-emitting diode 4 increases.
Now, this kind of remote commander is designed so as to become relatively small in size and light in weight so that this remote commander may become convenient for portable use. For this reason, since the small and light-weight remote commander may be operated by a suitable small battery such as a button cell, it has been requested that the remote commander should have less power consumption.
Although it has been proposed to decrease the current I flowing through the infrared light-emitting diode 4 in order to decrease the power consumption of the remote commander, when the current I flowing through the infrared light-emitting diode 4 decreases, the intensity of the light output Po decreases as shown in FIG. 3 with the result that a distance which an infrared remote control signal transmitted from the remote commander can reach is inevitably reduced. There is then a disadvantage that the remote commander will not be operated well.
To remove this disadvantage encountered with the related-art remote commander, there is proposed another example of a remote commander according to the related art as shown in FIG. 4. In FIG. 4, elements and parts identical to those of FIG. 2 are identified by identical reference numerals.
As shown in FIG. 4, the anode of the infrared light-emitting diode 4 is connected through a current-restriction first resistor 5a having a resistance of 6.8 ohms, for example, to one fixed contact 6a of a change-over switch 6, and the anode of the infrared light-emitting diode 4 is connected through a current-restriction second resistor 5b having a resistance of 16.8 ohms, for example, to the other fixed contact 6b of the change-over switch 6. A movable contact 6c of the change-over switch 6 is connected to the power supply at the terminal 7 to which the supply voltage Vcc is connected. Accordingly, when the movable contact 6c of the change-over switch 6 is changed-over, the remote commander may be switched to a normal power consumption mode (when the movable contact 6c is connected to one fixed contact 6a) and a low power consumption mode (when the movable contact 6c is connected to the other fixed contact 6b).
Therefore, even in the case the remote commander is not operated well when a low power consumption mode is applied, the disadvantage is prevented by switching over the low power consumption mode to a normal power consumption mode.
However, since the power consumption mode switching circuit is comprised of the second resistor 5b, the change-over switch 6 and the like as described above, the number of assemblies of the remote commander inevitably increases and extra cost is required so that the remote commander cannot be produced inexpensively.
Furthermore, let us consider a transmission distance which a remote control signal from this remote commander can reach is reduced when the remote commander is formed as the low power consumption type remote commander. Assuming now that the resistance of the first resistor 5a is 6.8 ohms and that the resistance of the second resistor 5b is 16.8 ohms, then we have:                normal power consumption:low power consumption=100:40        normal power consumption transmission distance:low power consumption transmission distance=1:0.63        
As a result, the distance which the remote control signal can cover is reduced and operability of this remote commander is degraded distinctly.